Dec DMX11--What was it?

[Paul Koning]

> On Oct 23, 2021, at 10:16 PM, Chris Zach via cctalk <cctalk at classiccmp.org> wrote:
> 
> Anyone know about the Dec DMX11? It was apparently a 64 serial line Mux that plugged into pdp11 Unibus systems and had a fair amount of both intelligence and insanity on board. Reason is I'm looking into some old documentation about late 1970's Tote systems for Asian race tracks and the system they were building was beyond astronomical in terms of insanity.
> 
> (As in an 8 way pdp11/70 system cluster, with 11/04's running these DMX11's to hundreds of terminals)

The April 1983 Options & Modules List (see http://www.bitsavers.org/pdf/dec/modules/modulesAndOptions/) shows it on page 156.  It is listed as a CSS product, 64 line mux controller (DMA both ways, so similar to the DH11) with separate 64-port line cards.  Three flavors of line card: 20 mA loop, "EIA" (presumably that means RS-232) and "Differential" -- perhaps RS-422?

Date is given as 08/1980, but that's the last update of the entry.  Status is "6".  The April 1983 document is missing its cover material which explains the codes, but the December 1975 edition (same Bitsavers directory) lists them.  "6" means "Obsolete, but can still be custom-built".

Given that it's a CSS device, documentation for it is likely to be hard to find, and software for it even harder.  For example, while RSTS would be a natural OS to support this (given that it can handle 128 terminal lines) it doesn't and as far as I know never has.

	paul